The present invention relates to a method of recording video data sent in digital broadcast or the like or stream data sent with a packet structure, a data structure of stream data suitable for this recording method, and information medium on which information is recorded using this data structure.
In recent years, TV broadcast has come into the era of digital broadcast. Accordingly, an apparatus for saving digital data of digital TV broadcast as they are irrespective of their contents, i.e., a so-called streamer, has been demanded.
The current digital TV broadcast uses an MPEG transport stream. In the future, an MPEG transport stream will be used as a standard one in the field of digital broadcast using moving picture.
In such digital broadcast, the contents (mainly, video information) to be broadcasted are time-divided into groups of data each having a predetermined size (e.g., 188 bytes) called transport packets, and broadcast data is sent in units of transport packets.
As a streamer for recording digital broadcast data, a home digital VCR such as D-VHS (digital VHS) or the like is currently commercially available. A streamer using D-VHS directly records a broadcasted bitstream on a tape. For this reason, a plurality of programs are multiplexed and recorded on a video tape.
Upon playback, all data are output from the VCR to a set-top box (digital TV reception apparatus; to be abbreviated as an STB hereinafter) when they are played back either from the beginning or the middle of the tape. In this STB, a desired program is selected from the output data by user operation or the like. The selected program information is transferred from the STB to a digital TV receiver, and is played back (playback of video plus audio and the like).
Since this D-VHS streamer uses a tape as a recording medium, it cannot attain quick random access, and it is difficult to quickly jump to a desired position of a required program so as to play it back.
As a promising candidate that can combat such shortcoming (difficulty of random access) of the tape, a streamer that uses a large-size disc medium such as a DVD-RAM or the like has been proposed. In this case, management data must be inevitably recorded together with broadcast data in consideration of random access, special playback, and the like.
When a DVD-RAM disc is used as an information storage medium, data are recorded in units of 2,048-byte sectors. On the other hand, digital TV broadcast adopts an MPEG transport stream, and stream data each of which stores video information are sent in units of 188-byte transport packets as minimum units of the transport stream. The size of this transport packet differs depending on digital TV broadcast stations and, for example, a given digital TV broadcast station sends data in units of 130 bytes. When such received transport packets are recorded in units of sectors on an information storage medium such as a DVD-RAM disc or the like as they are, the following problems are posed. That is:
1. Since 2,048 bytes as the sector size are not an integer multiple of the transport packet size (e.g., 188 bytes), a recording method of transport packets in a sector poses a problem.
More specifically, when transport packets are allocated in a given sector in turn from the first one, and the remaining area formed in this sector is handled as a padding area, a large number of wasteful padding areas are generated in units of sectors. For this reason, the stream data size that can be recorded on the information storage medium decreases by the padding areas in units of sectors. As a result, the practical recording capacity of the information storage medium decreases.
2. Stream data that have been video-compressed according to the MPEG format must be decoded by a decoder after they are played back from the information storage medium. In this case, the time interval between neighboring transport packets to be transferred to the decoder must hold that immediately after they were received from a digital TV broadcast station. For this reason, time interval information of each transport packet upon being transferred to the decoder is required.
3. Since transport packets recorded on the information storage medium have no identification information for identifying individual transport packets, there is no means for designating a specific transport packet upon search or edit.
4. When a DVD-RAM disc is used as an information storage medium, since data are recorded in units of 2,048-byte sectors, it is difficult to implement a partial erase process in units of transport packets.
5. Since stream data sent in digital TV broadcast have been video-compressed in accordance with the MPEG format, decoding must be started from an I-picture position. Therefore, a partial erase process at a specific video position must be done to have an I-picture start position at the head position of the data as a boundary position in practice. However, in information obtained by merely recording transport packets in turn in sectors, it is difficult to implement a partial erase process using the I-picture start position as the boundary position.
It is an object of the present invention to provide a recording method that can efficiently record stream data.
It is another object of the present invention to provide a data structure that can efficiently manage stream data.